PROJECT SUMMARY In addition to giving us our conscious perception of the world, the visual system is also responsible for regulating a wide-range of physiological processes such as circadian rhythms, sleep, attention, and mood. Thus, impairments in visual system function do not only result in loss of visual perception, but can also contribute to other conditions including depression, cognitive disorders, and circadian disorders. One major goal of vision research is to generate accurate and predictive models of principle circuit components, which will enable the development of treatments for these ailments and disorders. Retinal ganglion cells (RGCs) are the output cells of the retina and mediate a wide-range of visual behaviors and physiological processes by projecting to over 30 brain areas. In current models of the visual system, all RGCs relay excitatory signals to the brain by releasing glutamate. However, early evidence points to the presence of RGCs that are inhibitory and release the inhibitory neurotransmitter gamma-aminobutyric acid (GABA). This proposal aims to uncover the identity and function of GABAergic RGCs in the mammalian retina. The first aim of this proposed research is to identify and characterize GABAergic RGCs in the mammalian retina by utilizing mouse genetics and viral-mediated expression of fluorescent reporters. The second aim will determine mechanisms of GABA release by these RGCs and to determine the specific pathways through which they relay light information. Collectively, this research proposal will elucidate the circuits through with GABAergic RGCs influence physiology and will contribute to a more complete understanding of visual pathways.